The present invention relates generally to encapsulating or sealing of devices, such as organic light emitting diode (OLED) devices.
FIG. 1 shows an OLED device 100 which serve, for example, as a display in various types of consumer electronic products, including cellular phones, cellular smart phones, personal organizers, pagers, advertising panels, touch screen displays, teleconferencing and multimedia products, virtual reality products, and display kiosks.
The OLED device comprises a functional stack formed on a substrate 101. The functional stack comprises of one or more organic functional layers 110 between two conductive layers 105 and 115 which serve as electrodes (cathode and anode). The conductive layers are patterned as desired, for example, to form a pixelated, a segmented, or other types of devices. Charge carriers are injected through the cathodes and anodes via bond pads 150 for recombination in the functional layers. The recombination of the charge carriers causes the functional layer to emit visible radiation. The device is encapsulated with a cap 160. OLED devices require hermetic sealing since the active components, such as the cathode, are adversely impacted by moisture and oxygen.
Flexible OLED devices formed on polymeric substrates have been investigated. Due to low barrier performance of the polymeric material to moisture and oxygen, the substrate needs to be coated with a barrier. Typically the barrier comprises oxide or nitrides, such as aluminum oxide, silicon oxide, or silicon nitride. The barrier layer is formed on the polymeric substrate by physical vapor deposition (PVD) or chemical vapor deposition (CVD). When a barrier layer is deposited on a polymeric material, imperfections such as pinholes, cracks, and grain boundaries occur. Such imperfections adversely impact the barrier characteristics of the barrier layer. Multiple metal oxide layers have been proposed to improve barrier performance. However, the use of multiple metal oxide layers still has not satisfied the barrier performance necessary for OLED devices because pinholes or imperfections tend to propagate to the subsequent layers.
As evidenced from the foregoing discussion, it is desirable to provide improved barrier for OLED devices, particularly for flexible OLED devices.
The invention relates to a barrier stack for improved sealing of a device, such as an OLED device. The barrier stack comprises first and second base layers. The first base layer includes a flexible substrate having at least one of its surfaces coated with a barrier layer. The second base layer includes a flexible substrate having at least one of its surfaces coated with a barrier layer. The base layers are bonded together with a high barrier adhesive. In another embodiment, the barrier layer is coated with a liner layer to seal the micro and nano defects on the barrier layer to enhance the barrier property of the barrier stack. In yet another embodiment, a foil, such as aluminum or copper, is provided between the base layer.